1. Field of the Invention
This invention relates generally to an implantable device for the sustained delivery of a medicament and, more particularly, to a device and method for preventing restenosis following atherectomy.
2. Reference to a Related Patent Application
Reference is made to a copending patent application Ser. No. 08/002,209 filed Jan. 8, 1983, entitled: "Medicament Dispensing Stent for Prevention of Restenosis of a Blood Vessel" by the present inventor.
3. Prior Art
Cardiovascular disease (CVD) is the leading cause of death in the U.S. One commonly used method of treating CVD is angioplasty/atherectomy (mechanical or laser). While angioplasty/atherectomy is acutely successful in relieving the symptoms of CVD, the procedure is limited by a high rate of arterial reclosure or restenosis. Various methods of preventing restenosis have been tested with little success reported to date.
One possible treatment for the prevention of restenosis is Photodynamic Therapy (PDT), also known as Photoatherolytic (PAL) Therapy when referring to vascular applications of PDT. PAL Therapy requires the delivery of a photosensitizing drug to the stenosing atheroma which is selectively retained by the proliferating component of atheromatous plaques which is believed to be the cell type responsible for restenosis. Once sequestered in the problematic proliferating cells, the drug is converted from its ground or dormant state to an excited, highly toxic state by the absorption of light energy at a very specific wavelength. A currently preferred therapeutic modality consists of administering the photosensitizer (PS) drug systemically in a single-dose bolus. Since the drug is initially delivered to all cells of the body, a delay time is required to allow the PS drug to clear from normal cells while it is retained by the proliferating cells prior to activation with light.
Since restenosis is a complex process which can begin immediately after therapeutic intervention (angioplasty/atherectomy) and continue for months post intervention, it is desirable to provide a device and method capable of providing the sustained delivery of a PS drug to inhibit the proliferation of smooth muscle cells and ultimately to lyse the PS ladened cells with therapeutic light energy.
One approach to the problem of sustained long term drug delivery employs implantable biodegradable polymer/drug combinations in a variety of ways to achieve a controlled regular or continuous administration of the drug. Biodegradable polymers are useful as carriers for many different types of drugs because they serve as a temporary matrix to hold the drug, but do not chemically interact with the drug. As the matrix erodes, the drugs are released and can diffuse into the tissues.
In one prior art embodiment, a synthetic (non-biogenic) biodegradable polymer matrix is homogeneously impregnated with a medicament so that the medicament is released more or less continuously and uniformly as the supporting polymer matrix erodes. In another variation of this basic idea, a single reservoir of the drug or medicament in solution is encapsulated by a semi-porous polymer matrix. The drug diffuses continuously out of the reservoir, through the polymer, and finally to the intended delivery area. Metal stents coated with bioabsorbable synthetic polymer have also been used to deliver medicament but such metal stents are optically opaque and thrombogenic. In still a further variation, tiny discrete "pockets" of the drug are encapsulated throughout the synthetic polymer. If the polymer is biodegradable then it will completely dissolve thereby releasing all of the impregnated or encapsulated drug. The above prior an devices are known in the art and are made from synthetic polymers. The problems with implants fabricated using non-biogenic material are that such prior art implants are thrombogenic and being a "foreign body" stimulate the host's inflammatory response.
Such devices can also be constructed from naturally occurring biopolymers and derivatives thereof or biogenic tissue. Biological materials such as bovine and porcine tissues harvested from donor animals are commonly used for implantation into the human body. They are known to be non-thrombogenic and non-inflammatory. The porcine heart valve is one such example. Such biogenic tissues are well received and well tolerated by the host human tissues and, unlike biodegradable synthetic polymers, biogenic tissue implants are less likely to induce an inflammatory host response and are replaced over time by the host natural tissue produced in situ. Human tissues harvested from a human donor (autologous or heterologous) are also viable tissue types for this device.
Cancer is the second leading cause of death in the U.S. A stent-type device for the slow sustained delivery of an appropriate medicament to cancers on a luminal wall such as esophageal cancer, and a patch or plug-type of device for implantation within bulk tumors is desired. Preferably, such a stent, plug or patch should be minimally inflammatory, non-thrombogenic, optically transluscent, biologically compatible and capable of sustained drug delivery to a localized area of a tubular tissue over the period of time required to effect a permanent therapy.